The First House is concerned with the individual: it is about those things which make us unique. It also affects the way in which a person appears to others, such as their physical appearance.
Too many planets in the first house can lead to a personality which is too individualistic, and in which the person finds it difficult to reach out to others and to integrate their energies into their own life. Some planets may also have a negative effect on the way we interact with others: for example, Neptune in the First House may blur our awareness of the way in which we relate to others.